The ever increasing shortage of wooden raw material has strongly stressed the need for a better utilization of the raw material at the saw mills. To achieve the best possible yield and thus also the best possible economy it is, of course, a general desire that the logs should be properly adjusted in relation to the sawing members, viz. both with respect to the rotational position of the logs and with respect to the orientation and position of the longitudinal axis of the logs.
A key factor in this regard was previously an operator who was responsible for the proper adjustment of the logs. It was considered that a proper position has been reached when the log, by rotation thereof, has been turned into a best position with respect to any longitudinal curvature of the log and the log had been placed right in front of the saw. Usually, when this adjustment was carried out the operator was placed at distance of about 10 m away from the log end adjacent the saw. Sometimes, the operator had to his aid reference lines projected on the log, which lines to a certain extent facilitated the centering and side-adjustment of the logs. However, as the production rate should be high, such as 10-15 logs/min., and the distance to the log end was comparatively great, the centering and side-adjustment of the logs in relation to the sawing means often turned out to be rather bad, which resulted in waste of raw material and bad economy.
During recent years quite a few different methods and means have been proposed for an automatic measuring of the logs, to enable a subsequent turning of the logs into a proper rotational position, but as such automatic measuring equipment is comparatively complex and expensive, in many cases a visual classification of the logs is still applied.